Bullet proof chain guid guard yz250

I went to the BP site, thinking to tell you to go to it yourself, but, I couldn't find any instructions for the ( I presume you have a 2t?) 2t brace. 

So are these pics relevant? :

It seems I can just see the 2 holes you refer to, and, the Gap on the Swingarm in that pic seems to correlate to it.

So, I'd say , to get the full benefit of the brace, drilling and tapping the holes and bolts would be very useful.

I note that most other braces on so many bikes, just ty the 2  mounting tabs together, so to speak.

But, yours, with what appear to be extra mount points, offers even more strength, if you do the 2 bolts.

If you elect to go that way, bolt it on, and, using a drill ( 6mm / for 6mm holes?), I'd just use the holes as a initial guide / center / position finding, then, drill the 5mm holes for tapping the M6 thread. If the Swingarm is still on the bike, It might be a good idea to drill with a drill press, a 5mm hole through some thick piece of 'whatever', that you could clamp to the swingarm, to ensure straight drilling, and tapping after you've done the 'starter divot'.

 All not hard to do, just a bit fiddly. But, a bit fiddly, is better than having holes that aren't straight!

I made such bolt on things for my old Beastie (and other bikes) from RA alloy, when it was a std Pro Link rear end - I ride in really rocky / rutted terrain .

When I flipped the swingarm upside down, to make the PDS rear end, I welded on an 'outside' brace plate , as I swapped the original Chain Guide mounts and Disc mounts, from side to side. 

The other school of thought, of course, is that the standard TMD guide offers a bit of flex to return to straight if it gets a big hit. Rather than building it to "ultimate strength" so it won't bend?  At some point something has to give, right? Otherwise , try to call Billet Proof Designs...

The holes in the swingarm creating weakness - You've got the cross over bracing of the outside bolts to counteract that.

But, really, it would not be an issue.

Fit the brace, however you deem suitable for Your needs / riding, and use a (slightly) flexible guide, like that TMD, pictured or BRPs / other, which I use. 

I've  had far to many bent std Alloy guide 'cages' in my life - the second I could get a Nylon type guide, or, I could remove the std alloy plates if there was a substantial OEM 'inner', I went that way. 

Don’t do that.  Just go with the tm design works sx system.

I have one of those in my parts bin I have never used it, I have a tm designs one on and it gets bashed in the pnw rocks and holds up great. I did not know you had to drill into the swingarm to install them I thought it was just a puck? 

Those TM Designworks ones are meant to flex and return to shape, which is why they work so well. I think adding structural support might actually reduce the effectiveness of the part. 
Also, keep in mind that parts like the chain guide are meant to bend or break before the swingarm does. If you permanently bolt something rigid to it, you may damage the swingarm instead of the chain guide. Just my $0.02. 

Call BP - they are great guys that ride ......

Installed BPD chain guide reinforcements to every bike I've desert raced with for the last 2 decades, using both BRP and TM Designs guides. Drilling/tapping the extra mounting holes in the swingarm every time.

Not a one of them looked new after the first rock section I took them through. At one point, had to drill/ez-out a bolt out of the guide as the head had been ground completely off but the guide/frame tab never budged with the reinforcement.

Just rode a couple days ago, havent had a chance to wash the bike so go easy on me! The TMD chain guide and BPD swingarm protector align very well. Use the hardware provided by BPD. Ive ran this setup a on a couple of YZ250's I have. I never had to drill and tap anything. If you're drilling and tapping there is something wrong. Did you hit the chain guide mount before having protection and possible bent the mount?